Here's a little Mootools extension that you might find useful. I'm using it my StickyWin classes to allow the user to "pin" it in place so it won't move if they scroll.

PLAIN TEXTexecute this code
JavaScript:
$('fxTarget').pin()
$('fxTarget').pin()

drag to resize


Execute the example, then scroll. That's it. You can unpin it if you like:

PLAIN TEXTexecute this code
JavaScript:
$('fxTarget').unpin()
$('fxTarget').unpin()

drag to resize


(note, in this example because of the way my little fxTarget helper works, unpin will break the drag behavior, but that won't happen in other instances).

I've added .pin and .unpin to StickyWin, too.